In a liquid crystal display (LCD), because the liquid crystal layer itself has no function of light-emitting, it is necessary to provide a light source for the LCD to realize image display. In a transmissive type LCD, a backlight is used to provide a light source with a uniform luminance distribution for the liquid crystal layer.
In an existing backlight, generally, light-emitting diodes (LEDs) are used as light sources, and as the increase of the LED luminous efficiency, the number of light-emitting diodes used in a backlight is also gradually reduced. The configuration is from initially that two light bars with each consisting of a plurality of LEDs are respectively provided along two long sides of a glass substrate, developed to the case that one light bar consisting of a plurality of LEDs is provided along one long side of a glass substrate, and finally to the case that one light bar consisting of a plurality of LEDs is provided along one short side of a glass substrate, and thereby the number of LEDs used in a backlight is reduced.
FIG. 1 illustrates a schematic sectional view of a structure of a backlight module when an LED light bar is provided along a long side of a glass substrate. On a printed circuit board (PCB) 101, there is distributed an LED light bar formed by a plurality of LEDs 102. In the figure, a light guide plate 103 is located over the LEDs 102. In the backlight module, a back-plate is also comprised for fixing each assembly. Since the LED 102, as a spotlight source, has a limited light irradiation region, if too small number of LEDs 102 are employed in a backlight, there will exist a region on a light-incident surface of the light guide plate 103 that can not be irradiated by light, which will be prone to cause a dark area 105 appear on the screen corresponding to the backlight (i.e., the liquid crystal display screen), so that the luminance of the display screen is non-uniform, and thus display effect is adversely affected.